Kiln and method of operation



March 13,1945. E, BLAHA l2,371,420

KILN AND METHOD OF OPERATION Filed July 29, 1942 3 Sheets-Sheetl 1 All] vw p lNvENToR .EM/L l 6mm .Y BY WM ATTORNEY H u. El

1.141,1 Illll llllllllllllllllllllllllllll .1|.JI llllllllllllllllllll L@ l k March 13, .1945. E. BLAHA u KILN AND METHOD OF OPERATION INVENTOR fnv/L 5mn/r ff ATTORNEY y Filed July 29, 1942 Patented Mar.l 13, .1945

KILN AND METHOD or OPERATION Emu Biene, Cheltenham, Pa., assigner to' seme Corporation of America, a corporation of Penn- Sylvania Application July 29, 1942, Serial No. 452,761

19 Claims.l (Cl. 25-142) One general object of the present invention is to provide an improved method of heating the high temperature or ring zone of a kiln at temperatures higher than have heretofore been customarily produced, and another general-object of the invention is toprovide a simple and effective continuous' tunnel kiln structure adapted for use in the practice of said kiln heating method. f

A more specifically stated object of the inven-` tion is to provide a kiln with open fire" heating provisions adapted to maintain ring zone temperatures of 30003600 F., or even higher in some cases. A still more specific object of the present invention is to provide a kiln with novel provisions for the recuperative preheating of all, or a substantial portion, of the combustion supporting air.

My improved method of kiln heating is characterized by the introduction of upwardly directed burning streams or jets of combustible fuel and combustion supporting gas into a high temperature or firing zone of the -klln chamber, at closely spaced points distributed along the length of the kiln, and preferably with jet velocities high enough for the jets to form side by side streams which flow upward along the side Walls of the kiln chamber and thence inward along the kiln chamber roof toward the longitudinal center line of the latter, and is characterized by the withdrawal of products of combustion from the kiln chamber at a multiplicity of points distributed along the length of and adjacent the lower edges of the side walls.

In a kiln chamber heated as described, all or practically all of the inner side wall and roof surface of the firing zone of the kiln is heated to incandescence and the work is largely heated by radiation from said surface and from the adjacent burning jets.

y In the preferred form of the invention, the fuel gas and combustion air forming the burning jets are highly preheated, and my improved kiln is characterized by its preheating provisions. In the preferred construction illustrated, a portion of the available heat in the products of combustion withdrawn from the firing zone is utilized in recuperatively preheating streams lof combustion air passing into the different'burning jets and another portion ofthe available heat is utilized in a preheating zone of the kiln.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages,.and speciiic objects attained with its use, reference should be had to the accompanying drawings and ldescriptive matter in which I have ing means.

illustrated and described a preferred embodiment of the invention.

Of the drawings: Fig. 1 is a diagrammatic plan, partly in section, of the preheating zone portion of a continuous tunnel kiln; y

Fig. 2 is a diagrammatic plan, partly in section, of the intermediate firing zone portion of the kiln;

Fig. 3 is a diagrammatic plan, partly in section, of the 4cooling zone portion of the kiln;

Fig. 4 is a vertical section on the line 4 4 of Fig. 2; v

Figs. 5, 6 and 7 are partial plan secons on the lines 5 5, 6 6 and 1 1, respectively, of Fig. 4;.

Fig. 8 is a partial vertical section on the line 8 8 0f Fig. 1; and

Figs. 9, 10 and 11, are partial vertical sections on the lines 9 9, IIJ-Ill, and Il ll, respectively, of Fig. 3. y

The continuous tunnel kiln A shown by way of example in the drawings, comprises preheating, high temperature and cooling zones or sections A', A2 and A3, shown somewhat diagrammatically in Figs. 1, 2 and 3, respectively, through which the goods or wares treated are progressively moved from the inlet end A* to the exit end A5 ofthe kiln chamber by suitable goods advanc- 'I'he latter, in the conventional form shown, comprises a series of kiln cars B, having refractory body portions which extend vertically through a slot A6 formedl in the bottom wall of I the kiln chamber, as shown most clearly in Fig. 4. The refractory body portion of each car is carried by a metallic car under structure B', having wheels B2 which run on track rails C extending longitudinally of the kiln chamber. As shown, the track rails aregbeneath the refractory body of the kiln which is supported above the kiln building floor level by a metallic framework D.

The cars B may be moved through the kiln chamber at the proper speed by mechanism which may be of one or another of various well known types and need not be illustrated or described hereinll As shown in Fig. 4, the walls of thel kiln chamber bottom wallslot A6 and the sides of the refractory carbodies are relatively out of the kiln chamber through the bottom slot A6, and to the same end the kiln is provided with sand sealing means, but the leakage preventing expedients need not be further described herein as they are well known in the art and their particular form constitutes no part of the present invention. y

The novel means provided to heat the kiln, comprise a series of vertical burner chambers or wells E arranged in two rows, one at each side of the kiln chamber and each extending along the full length of the ring zone kiln section A2. lEach burner chamber E is formed in a corresponding ledge or bench portion Fof the refractory kiln structure. The two benches F at 'the opposite sides of the kiln chamber constitute the portions of thekiln chamber licor not formed by the refractory bodies of thel kiln cars B.

In the preferred construction shown, each burner chamber E receives uld fuel at its lower end through the outlet port G' of an individual upwardly inclined supply passage G, and' receives combustion air through an individual transverse channel H. Each channel H opens at its inner end into the corresponding burner chamber E adjacent the lower end of the latter, and has its outer end connected to the lower end of a corresponding recuperator tube or pipe I of ceramic material which extends up from the bench level through the corresponding side wall of the kiln chamber and above the top of the refractory kiln structure. Each pipe I is connected to an individual valved branch J1 from an air supply main J, at the same side and extending longitudinally of the kiln. Ordinarily, each of the two mains J is connected to a source (not shown) of air under a pressure somewhat above that of the atmosphere.

Each combustion air supply pipe I extends axially through an individual vertical recuperator channel K of larger diameter, and formed in the corresponding side wall of the kiln chamber. Each channel K extends upward to a level above the kiln chamber, but below the top of the kiln structure, and has a laterally bent upper end K1 which opens into the adjacent one of two flues K2 formed in the kiln roof structure at opposite sides of a division wall K3. Each ue K2 extends longitudinally of the kiln for the full length of a kiln ring zone A2, and discharges partially cooled, but still hot, products of combustion into a corresponding preheating zone flue, as hereinafter described. Some, at least, of the channels K may be provided with individual slide brick outlet dampers K10, as shown in Fig. 4, which may be adjusted to regulate the distribution of upow through the channels.

The different channels kiln chamber open at their lower ends into a common longitudinal channel K4 formed in the corresponding bench F and extending along the full length of the firing zone. Each channel K4 re ceives hot products of combustion from the kiln chamber through a series of ports K5. The ports K5 and tubes I at each side of the kiln chamber alternate along the length of the firing zone. Each port K5 forms the outlet end of a correspending transverse channel formed in the bench and connected at its inner end to the kiln chamber through a corresponding inlet port K. The ports K6 at each side of the kiln chamber alternate along the length of the firing zone with the burner wells E. y

In the preferred' construction illustrated, each channel G is the bore or axial passage of a suitable refractory ceramic tube L, which has an outer end portion which is of larger diameter K at each side of thel than its inner end portion, and extends through an air or gas space in the kiln masonry. The tube L is mechanically connected at its outer end to the inner end of a corrugated metal tube L which has its outer end connected`through a metallic kiln armor member M to a corresponding Valved branch N' from a supply main N extending longitudinally of the kiln along the corresponding side of the firing zone. As shown in- The described connections between the supply mains N and the burner chambers E are designed to accommodate the very considerable relative expansion of the kiln structure and conduit parts due to temperature changes, and thus avoid leakage of the fluid fuel supplied by the mains N, even .though the pressure in the mains may be several pounds above the pressure of the atmosphere.

In the preferred use now contemplated of the kiln shown in the drawings, the fluid fuel supplied by the mains N will ordinarily consist of a suitablev available gas`mixed with some of the air required for complete combustion of the gas. If the latter is a strong gas such as natural, city, or coke oven gas, it may well have mixed with it from l0 to 20% of the total air required for its combustion, the remaining 90% to 80% being supplied through the recuperator pipes I. The mixture of'a significant portion of the combustion air with the fuel gas supplied to the burner chambers E, speeds up the rate of combustion in the burner chambers and eliminates the risk of objectionable deposits of carbon cracked out of the fuel gas in the channels G. The gas and air mixture passing through the channels G is subjected to a substantial preheatnig eiiect', but ordi` narily the mixture temperature attained in the channels G will be appreciably lower than the temperature to which air is preheated in the pipes I. For the attainment of high kiln chamber temperatures with a weak fuel gas, such as producer gas supplied through the passages G', the gas should have little or no combustion air mixed with it.

Ordinarily, in the construction of'my improved kiln, the customary practice will be followedof using highly refractory ceramic materials inthe inner portions of the kiln chamber walls and of forming the outer portion of the kiln chambers walls of materials having good heat insulating propertiesbut not adapted to withstand as high temperatures as the more refractory inner wall materials. For the .extremely high ring zone temperatures required in some contemplated uses of the kiln, I line the kiln chamber with thin curved tiles O of some suitable high refractory material such as beryllium oxide. With temi peratures somewhat lower, but still higher than are customary in tunnel kilns, I may form the tiles O of the refractory silicate known as sillimanite. Generally such tile materials have relatively little mechanical strength at high temperatures, and I advantageously construct the kiln chamber firing zone with a roof arch of Gothic form, as shown in Fig. 4, rather than of the more usual rounded form.

As the goods pass from the inlet end A4 of the ykiln to the firing zone, the goods temperature is progressively increased primarily as a result of the heating action of the ues P, one formed in and extending longitudinally of each side wall of the preheating section A of the kiln chamber. The hot gases which the i'lues K2 receive from the recuperatorpas'sages K, pass fromthe fluesjK2 into the corresponding -flues' P through vertical passages Q formed in the .portion =of the corresponding side wall ofthe kiln chamber adjacent the junction of the preheating and firing sections A' and A2, as bestshown in Figs. 1 and 2. As shown in Figs. 1 and 8, each flue P is separated from the kiln chamber by a thin wa11 formed by refractory tiles P arranged end to end along the length of said ue, and each extending from the top to the bottom of the ilue. As shown the tiles P are provided at their^upper and lower ends with 'inturned horizontal anged portions P2. The tiles P may be formed of any suitable refractory material, but advantageously 'are of a material such as silicon carbide which has good heat conductivity at its' normal operating temperatures. At the inlet end of the kiln, the flues P communicate with vertical passages R which are connected to a chimney or exhaust fan (not shown) forwithdrawing products of combustion which have lost most of their original heat content before they reach the passages R.

In the construction of the cooling zone section of the kiln, use may be made of expedients commonly employed to secure a suitably rapid and suitably graduated reduction in the ware temperatures which may pass into the cooling zone from the ring zone at a temperature in excess of `3000 and which should be cooled down to a. much lower temperature, which in some cases, is'not higher than two or three hundred degrees F., before passing out of the exit end A of the kiln.

As sli-own in Figs. Band 9, a short portion of the cooling zone of the kiln immediately adjacent the firing zone is formed with relatively thick side walls having adjacent their outer sides open ended vertical cooling channels S, the outer walls of which may be formed by corresponding portions of the metallic kiln casing m. The channels S are shown as open at their upper and lower ends and operate as chimneys to cause a continuous upflow through' the channels of atmospheric air.

In an intermediate section of the cooling zone, the side walls of the kiln chamber are thinner than in the section previously described and are formed with Vertical'cooling channels T separated by ceramic material walls from' the outer casing m, as shown most clearly in Fig. 10. The channels T open to the atmosphere at their upper ends and open to the atmosphere at their lower ends through lateral ports T', and act like chimneys.

In the exit end portion of the cooling section, as shown most clearly in Fig. 11, the top and side walls of the kiln chambers are formed by metallic conduits U and UA respectively, shown as rectangular in cross-section and each provided with inlet and outlet connection U and U2, which may be associated with suitable fan means for creating aforced circulation of air through the conduits U and UA.

In the normal contemplated operation of the kiln shown in the drawings and just described, combustion supporting air and a suitable mixture of air and gas are supplied by the mains J and N under pressures which mayvary with operating conditions. Preferably said pressures are high enough under all normal operating conditions to cause the products of combustion and vburning gases to issue from the upper ends of the burner chambers E in the form of jets`each having a velocity high enough to maintain a continuous upflow along the side walls of the kiln chamber from the mouths of the burner cham--v bers Vli.' to the apex of the kiln chamber roof arch, and to cause downflow 0f the heating gases from the apex of the kiln chamber roof lto the outlet ports K6 in streams which alternate with, but are not as sharply defined as` the uprising streams or jets issuing fromv the 'burner chambers E.

`The present invention is adapted for use in kilns employed for a wide variety of high temperature operations, and when so used may include various expedients which experience has shown to be necessary or desirable in the operation of a continuous tunnel kiln for such purposes. For example, in the use of my improved kiln for firing ceramic products giving oi substantial volumes of Vapor or jsmoke" as they are preheated, the preheating zone of the kiln may be provided with smoke discharging means. Furthermore, kilns constructed in accordance with the present invention may in some cases, advantageously .include provisions of knownform for regulating kiln atmosphere circulation.

As will be understood, also, the relative amounts of fuel gas and combustionsupporting air supplied to the kiln burners may be regulated to maintain a neutral, reducing or oxidizing kiln atmosphere, as conditions make desirable. It is to be noted, however, that with the relatively large number of burners E, theaccurate regulation of the amounts of fuel and air supplied to each burner and the high combustion temperatures characteristic of my improved kiln, combustion is so rapid and complete that to maintain a neutral kiln chamber atmosphere, the ratio of combustion supporting air to gassupplied must be ahnost precisely that theoretically ref quired for complete combustion.

In the normal contemplated operation of any particular kiln of the type disclosed, the goods are progressively advanced through the kiln chamber at a rate determined by the conditions of operation, and the relative amounts of gas and combustion supporting air supplied to the dinerent burner chambers E distributed along the length of the ring section of the kiln 'are regulated as required to maintain the temperature curve, or temperature gradation along the length of the kiln, considered desirable for the particular use to which the kiln is being put.

In general, the rates at which gas and combustion supporting air are supplied to the difierent burners E, and the rate of goods movement through the kilns, should be so related that the goods temperature will lprogressively increase, but not necessarily at a uniform rate, as the goods move to a point which is intermediate the ends of the kiln firing zone and which is usually nearer the exit end than the inlet end of that zone, and so related that a fairly constant goods temperat'ure will be maintained as the goods move from said point to the exit end of the firing zone of the kiln.

The particular kiln shown in thedrawings was devised for use in ring steatite parts, used in radio receivers andA for vother purposes, to a temperature of 3200 F- by the combustion of city gas ofA about 530 B'. t. u. per cubic foot and with flowing upward along and in proximity to the side walls of the combustion chamber and thence inward along and in proximity to the kiln chamber roof to the center line of the latter, contributes to the maintenanceA of high temperatures and good heat distribution. With the burning and highly heated gases moving in relatively thin streams along the side and roof walls of the kiln chamber, allor practically all olf the inner wall surface of the high temperature zone of the kiln chamber is heated to incandescence, and the major portion of the heat absorbed by the goods passing through the high temperature zone of the kiln is transmitted to the goods by radiation from said wall surface and from theburning and highly heated gasesimmediately adjacent said surface.

The preheating of the combustible constituents passing to the burner E through the channels G and through the pipes I .and channels H, is substantial, and contributes to the maintenance of desirable combustion conditions and to the attainment of high temperatures.

It is usually desirable to decrease the percentage of air in the mixture supplied to the wells E through the channels G as they B. t. u. Value of the gas diminishes, and when a fuel gas as weak as ordinary producer gas is used to produce relatively high temperatures, little or no air should be mixed with the gas supplied through the channels G. With rich gas, however, it is ordinarily practically feasible to maintain the desired temperature conditions with considerable Variations in the relative amounts of combustion supporting air supplied through the channels G and H.

By suitable regulation of the air-fuel ratio in the mixture supplied through the channels G and of the relativerates of flow through the channels G and H, it is possible to signicantly vary the longitudinal temperature gradients oi the jets discharged into the kiln chamber from the burner wells E. Such regulation of the jet temperature gradients contributes to the maintenance of desirably relatedtemperatures at different levels. The temperature drop along the length of the firing zone, may be regulated by adjustment of the valves in the different supply branches J and N', desirably accompanied in some cases by related adjustments of the slide brick dampers KW in the roof fiues K2.

For the particular use for which the kiln shown in the drawings was devised, under maximum load conditions the air in the supply main J may be under a pressure of about l pound per square inch above atmospheric pressure, and the pres-- sure in the air and gas mixture supply main N may be about 3 pounds per square inch above at,- mospheric pressure, and said mixture may in clude about,50% of lthe combustion supporting air required. Under such conditions the gauge pressure of the kiln chamber atmosphere in the high temperature zone in the kiln at the bench level may be positive and from about two-tenths of an inch to about one-half oan inch of water.

As will be understood, the operational data. just given is given merely to illustrate the suitable operating conditions for one particular use of a kiln of one particular design and size.

With a kiln chamber shaped to provide uprising side walls which merge into inwardly inclined roof sections intersecting at an angle, use in the high temperature zone is advantageously made of wall lining tiles 0 which extend, as shown in Fig. 4, from the bottom of the kiln chamber to the apex of the vaulted roof. Such tiles may be formed of beryllium oxide or other material having little mechanical strength, but which is substantially more refractory than the load carrying kiln chamber walls which they line and shield against the high kiln chamber temperatures.

While in accordance with the provisions of the statutes, l have illustrated and described the best from of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention, as set forth in the' appended claims, and that in some cases certain features of my invention may be used to advantage ywithout a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of heating an elongated high temperature zone of a continuous tunnel kiln having kiln chamber side and roof walls of refractory material, which comprises upwardly directing burning jets of preheated fuel gas and combustion supporting air into the kiln chamber at closely spaced points distributed along the length of said Zone and adjacent the lower edges of its side walls, and withdrawing products of combustion from said zone at a multiplicity of closely spaced points distributed along the length of said Zone and adjacent the lower edges of said side walls.

2. The method of heating an elongated high temperature zone of a continuous tunnel kiln having kiln chamber side and roof walls of re- .fractory material, which comprises upwardly directing burning jets of preheated uid fuel and combustion supporting gas into the kiln chamber at closely spaced points distributed along the length of said zone and adjacent the lower edges of said side walls, and forming each jet by combining, immediately adjacent said points, two separately preheated supply streams, one of which includes the fluid fuel and a portion of the combustion. supporting gas and the other of which includes the remainder of the combustion supporting gas.

3. The method of heating an elongated high temperature zone of a continuous tunnel kiln having kiln chamber side and roof walls of refraetory material, which comprises passing preheated fiuid fuel and combustion supporting'gas into the kiln chamber at closely spaced points distributed along the length of said zone adjacent the lower edges of its side walls, and forming burning streams of the fluid fuel and combustion supporting gas which iiow side by side and upward from said points along said side walls approximately parallel to vertical planes transverse to the side walls of and thence along the roof wall toward the longitudinal center line of the latter.

4. A' continuous tunnel kiln having a kiln with uprising side walls and having a multiplicity of burners `distributed at lshort intervals along the length of said zone and opening into the kiln i chamber adjacent the lower edge of each of said side walls and each adapted to Adischarge an upwardly directed burning jet alongside thel adjacent side wall, and means for supplying preheated iiuid-'fueland preheated combustion supporting air to each burner at separately regulable rates. y

5. A continuous tunnel kiln having a kiln chamber comprising an elongated ring zone with uprising side walls and having amultlplicity of burners distributed at shortintervals along thelength of said zone adjacent the lower edge of each of said sidewalls and each adapted to disf ter, and having kun chamber side waus and re-` charge an 'upwardly directed burning jet alongl side the adjacent wall, means for supplying fuel gas and combustion supporting air to each of said burners, and means for withdrawing products of combustion from said zone at a multiplicity of points distributed along the length of said zone and adjacent the lower edges of said walls.

6. A -continuous tunnel kiln having a kiln y' chamber comprising an elongated ring zone with uprising side walls and having a multiplicity of burners distributed at short intervals along the length of said zone and opening into the kiln chamber adjacent the lower edge ofeach of said side walls, and having a plurality of outle't ports distributed at short intervals along the length of said zone and opening to the kiln chamber adjacent the lower edge of each of said side walls,

and upiiow channels respectively adjacent the diiierent downiiow channels 'and in communication at their lower ends with respectively adjacent lower portions of the kiln chamber, and means for Asupplying fuel gas to the different burners comprising a separate supply channel for each burner.

8. A continuous tunnel kiln structure having a multiplicity of closely spaced burners distributed along the lower portion of a high temperature kiln chamber zone adjacent each side of the latter and having wallsat the sides of the kiln chamber and recuperators therein comprising a separate downflow combustion supporting air supply channel for each of said burners and in communication at its lower end with the latter and upiiow channels respectively adjacent the diilerent downow channels and in communication at their lower ends with respectively adjaalong the lower portion of a high temperature kiln chamber zone adjacent each side of the lat-f for each burner and incommunication at its lower end with the latter and upflow channels respectively adjacent the diiIerent downflow channels, and having a ijlue in the lower' portion of each side wall extending along the length of said zone to which the lower ends of the said upilow channels in the same side wall are connected, each of said ilues lbeing in communication at points distributed along its length with respecA tively adjacent portions of the kiln chamber, and means for supplying iiuid fuel to the dierent burners.

10. A continuous tunnel kiln structure comprising side walls at the opposite sides of an elongated ring zone section of the kiln chamber and benches respectively adjacent and at the inner sides of the lower portions of said sidewalls and `having a series of closely spaced burner wells formed in each bench and each open `at its upper .end to the kiln chamber, a separate combustion supply conduit connection to each of the differ v ent burner wells.

11. A continuous tunnelkiln including aligned preheating and high temperature kiln chamber zones and having a multiplicity of closely' spaced burners distributed along the lower portion of said high temperature zone adjacent each side of the latter, and having a roof formed 'with a flue space over the high temperature zone and having side walls and recuperators therein at the sides of the high temperature zone comprising a separate downow combustion supporting gas supply channel for each of said burners and in communication at its lower end with the latter and uptlow channels respectively adjacent the different downfiow channels which are in communication at their lower ends with respectively adjacent lower portions of the kiln chamber and in communication at their upper ends with said iiue space, preheating zone heating means in communication with and receiving heating gases from said ue space, and means for supplying duid fuel to the diierent burners.-

cent lower portions of the kiln chamber, and means for supplying fuel gas to the diierent burners comprising a separate supply channel for each burner, the last mentioned channel having a wall of ceramic material and extending through and absorbing heat from a heated portion of the kiln structure.

. 9. A continuous tunnel kiln structure having a multiplicity'of closely spaced burners distributed 12. A continuous tunnel kiln as speciiied in claim Il, including dampers for regulating communication between said upflow channels and ilue space.

13. A continuous tunnel kiln structure com- .prising side walls at the opp'osite sides of an transverse channel connecting the lower end of the downilow channel tothe corresponding burner well, upilow channels in said 4side walls annular in cross section and each surrounding a corresponding one of said downow passages, a longitudinal iiue in the lower portion of each side wall to which the lower ends of the annular upow channels in said wall are connected, and transverse connections from said flues to the kiln chamber distributed along the length of the ring zone section.

14. In the method speciied in claim 1, the further step which comprises transferring heat from the products of combustion withdrawn from the kiln chamber at each of the last-mentioned points and passing upwardly therefrom, to combustion supporting air passing downward and thence into the kiln at a closely adjacent one of the first-mentioned points.

15. In the art of heating a zone of a kiln having' a chamber formed by opposed side and roof walls of refractory material, the improvement which comprises directing upwardly burning streams of combustible fuel and combustion supporting gas in the chamber at spaced regions distributed along the zone adjacent to the lower edge portions of the side walls, and withdrawing products of combustion from the chamber at a number of spaced regions distributed along the zone adjacent to the lower edge portions of the side walls.

16. In the art of'heating a zone of a kiln having a chamber formed by opposed side and roof walls of refractory material, the improvement which comprises iiowing combustible fuel and combustion supporting gas to a plurality of spaced regions distributed along the zone adjacent to the lower edge portions of the side walls, directing burning streams of the combustible fuel and combustion supporting gas upwardly from said regions alongside the side walls, withdrawing products of combustion from the chamber at a number of spaced regions distributed along the zone adjacent to the lower edge portions of the side walls, and passing the products of combustion withdrawn from the chamber in heat exchange relation with the combustion `supporting gas flowing to the first-mentioned regions.

17. A kiln comprising a chamber providing a firing zone having opposed vertically disposed walls, a number of burners distributed at intervals tible fuel and combustion supporting gas to the burners, said burners being formed and disposed so that burning streams of the combustible fuel and combustion supporting gas may be discharged upwardly therefrom alongside the walls. and means whereby products of combustion are withdrawn from the chamber at anumber of regions distributed along the zone adjacent to the lower edge portions of the walls.

18. Kiln' structure comprising refractory material forming a chamber providing a'flring zone having opposed vertically extending walls, a number of burners distributed at intervals along the zone adjacent to the lower edge portions of said walls, heat exchangers having first and second passages, the heat exchangers being embedded in the refractory material, means for supplying combustible fuel to the burners, means including the iirst passages of the heat exchangers for supplying combustion supporting gas to the burners, said burners being formed and disposed so that burning streams of the combustible fuel and combustion supporting gas may be discharged upwardly therefrom alongside the walls, and means including the second passages of the heat exchangers for withdrawing products of combustion fromthe chamber at a, number of regions distributed along the zone adjacentv to the lower edge portions of the walls.

19. A kiln comprising a chamber providing a firing zone having opposed side and roof walls formed of refractory material and constituting the load carrying walls of the kiln, a number of burners distributed at intervals along the'zone adjacent to the lower edge portions of the side walls, means for supplying combustible fuel and combustion supporting gas to the burners, said burners being formed and disposed so that burning streams of the combustible fuel and combus- 40 tion supporting gas may be discharged upwardly along the zone adjacent to the lower edge por- 5 tions of said walls, means for supplying combustherefrom alongside the side walls, means whereby products of combustion are withdrawn from the chamber at a number of regions distributed along the zone adjacent to the lower edge portions of the side walls, and wall lining tiles at the inner surfaces of said side and roof walls, the wall lining tiles being formed of material of less mechanical strength 'and more refractory than the refractory material forming theload carrying walls of the" n.

EMIL BLAHA. 

